High frequency coupling system



June 30, 1936. 'Y D, E. HARM-:T11 i i 2,045,910

HIGH FREQUENCY COUPLING SYSTEM INVENTOR 3 97990.70 waumfvslir ATTORNl-:

`hme 30, 1936. D. E. HARNETT HIGH FREQUENCY COUPLING SYSTEM Filed May 31, 1954 5 Sheets-Sheet 2 INVENTOR DAN/EL E. HAH/VET?" BY @und l June -30, 1936.

D. E. HARNET-r HIGH FREQUENCY COUPLING SYSTEM Filed May 31, 1934 3 Sheets-Sheet I5 EE J7 lf l lNvENToR AN/EL E. HARA/ETT BY QW' 9% Lw.- FW

` ATTORNEY Patented June 30, 1936 I UNITED STATES 2,045,910 nien FREQUENCY coUrLnvG SYSTEM Daniel E. Harriett, Tuckahoe, N. Y., assignor to Hazeltine Corporation, a corporation of Dela- Ware Application May l31, 1934, Serial No. 728,438

2s claims. (ci. 17a-44) 'Ihis invention relates to improvements in tuned high-frequency coupling systems, applicable to radio broadcast receivers, for selectively relaying carrier Wave signals.

5 An object of the invention is toprovide a tuned coupling system, the selectivity or resonance band width of which is adjustable by means of a unitary control in such manner as to maintain the resonance band symmetrically disposed with respect 10 lto the carrier frequency.

/ In Ythe art of radio broadcasting speech and music, a high degree of selectivity or signal discrimination is, to a. degree, incompatible with perfect reproduction of the originating acoustics. Fidelity in reproduction of speech or music necessitates substantially uniform overall transmission of carrier frequency sidebands from approximately 50 cycles to between 5000 and 15000 cycles. depending upon the character of the program. Where both upper and lower sidebands are transmitted the response characteristic of thereceiver should be substantially uniform for double these values. It will be appreciated, however, that band widths of this order are not always "obtainable with freedom from interference du'e to stations operating on broadcasting channels adjacent the station selected, or from static.

At aparticular reception locus and time, certain stations may be received substantially free from interference while others may be subjected to the severe competition of powerful or nearby stations operating on adjacent channels. For receiving stations of the flrst type it is desirable that the selectivity of the receiver be decreased l in order that signal reproduction be made as perfectas the system is capable of providing. If, however, a shift in tuning is made toa station of the secondtype, it thereupon becomes highly desirable to sacrifice some tonal quality by increas- 4oing the selectivity -to the end of freedom from interference.

The present invention has for its primary object the provision of a tuned coupling system, applicable either tothe reception frequency or intermediate frequency stages of a broadcast receiver, wherein the selectivity or resonance band width of the system may be adjusted' as'desired within limits, without necessity for retuning. As applied more particularly to the intermediate frequency stages of a superheterodyne receiver, it is highly 'important that this change in selectivity be accomplished Without shifting the resonance band in the frequency scale. To this end the present invention maintains the resonance band symreactively coupled through capacity or inductance adjustable within limits such as voptionally to change the overall selectivity from the narrow, single humped response, characteristic of optimum or less than optimum coupling between tuned circuits, to the relatively broad, doublehumped response, characteristic of over optimum coupling.

Seme methods of varying the coupling between tuned circuits tend to shift the center or median frequency of the band as the band width is altered. If the predominant portion of the selectivity of the receiver is shifted a like amount, the shift may be compensated by changing the setting of the main tuning control. Even though only a portion of the selectivity is varied by the coupling adjustments the shift in frequency may usually be compensated sufficiently for all practical purposes by readjusting the main tuning control. It is desirable, however, to be able to tune the station in and then make appropriate selectivity adjustment without having to reset the tuning; in other words, to make the tuning and selectivity tuning controls independent of each other.

A feature of the present invention resides in the association with the individual resonant circuits constituting each coupling system, of compensating reactances responsive to variation of coupling therebetween for maintaining the resonance band disposed, as stated, in substantial symmetry to the reception or intermediate frequency as the case may be. These compensating reactances may take the form of adjustable reactances in series with, or in shunt to, the principal tuning reactances of the coupled circuits. Where the resonance band width is adjustable in steps, these compensating reactances may be semi-adjustable elements which are suitably adjusted once for all in relation to their associated coupling reactance. Or, in the quantity production of radio receivers, the compensating and coupling reactances may be permanently fixed in value as determined by the receiver design.

On the other hand where, as is the case in accordance with one modification of the present invention, a capacitive coupling between tuned circuits is employed which is continuously adjustable throughout a range of values, it is desirable that the correspondingl compensating reactances capacities should likewise be so continuously .varied by the coupling adjustment as to prevent `substantial shifting in frequency of the 'resonance band. As a further feature of novelty, the present invention provides a continuously variable condenser of original construction adapted to achieve this objective.

Referring now to the drawings:

Fig. 1 shows diagrammatically as applied to'a radio broadcast receiver, tuned coupling systems in accordance with the present invention employing capacitive coupling and compensating capacitive reactances adjustable 'in steps by a unitary control. l y

Fig. 2 depicts the symmetrical disposition of the resonance band with respect to the median frequency as its Width is with the invention.

Fig. 3 is a modication of the Fig. 1 coupling system. y

Figs. 4 and 5 show coupling systems wherein the resonance band width is adjustable in steps by -means of inductive rather than capacitive Fig. 6 illustrates diagrammatically, application of the novel variable condenser structure herein to a. second type of capacitively coupled system, for continuously adjusting the band width while preventing substantial shifting of the band in the frequency scale.

Fig. 'l is a simplified coupling system generic to the modifications of Figs. l, 3, 4, and 5.

Fig. 8 isa generic simplified circuit diagram embracing the Fig. 6 type of coupling system.

Fig. 9 is a front elevation of the novel condenser structure illustrated diagrammatically in Fig. 6, a portion of the structure being broken away to show the assembly.

Fig. 1'0 is a section along I-ID of Fig. 9.

Fig. 11 is a circuit diagram, similar to that of Fig. 6 of a coupling system employing va condenser structure similar to that of Figs. 9 and l0.- but provided with additional stator and rotor plates.

Fig. 12 is-a view in sectional elevation, corresponding to Fig. 10, of the condenser structure illustrated diagrammatically in Fig. l1.

Referring to Fig. l,- there are shown an antenna I and ground 2, constituting the input to a superheterodyne radio broadcast receiver, wherein the Vradio frequency stages and the 0scillator-modulator portion of the system are shown diagrammatically by the rectangle 3. The modulator anode (not shown) is connected by lead I to the upper terminal of a coil Lx', the lower terminal of which is grounded at 5 through the modulator plate battery 6. The modulator cathode (not shown) is effectively grounded at l, so that the modulated output is impressed across coil Lx'. Coil Lx' constitutes the input to a tuned coupling system T1 Ain accordance with the present invention and described more-fully hereinafter, the output of which comprises a. similar coil Ly' connected between ground 8 and the grid G1 of a vacuum tube V1 operating as a stage of intermediate frequency amplification. The cathode of tube V1 is effectively grounded through the biasing impedance 9.

A coupling system T2 similar to T1 relays the signals from the output of tube V1 tothe input of l a second stage of intermediate frequency amplification, tube Vz. To this end the anode A1 of tube V1 is connected by lead IIJ to the upperterminal of an input coil Lx similar to Lx', the lower terminal of which is grounded at Il varied ,in accordance through the plate battery I2 supplying tube V1. Output coil Ly of system T2 is connected between ground I3 and over lead I! to the grid G2 of tube Va, the cathode K1 of which is groundedr through the biasing impedance I5.

The signal voltage developed between the anode Az and grounded cathode K2 of tube V2 is grammatically by rectangle I8, the output 'of which extends to the usual loud speaker 20.

The coupling system T2 of Fig. l comprises, in

addition to the input and output coils Lx and Ly,

a pair of tuning condensers Cx and Cy, connectedv to the coils respectively, and several additional condensers C., C11, and Ccvassociated with contacts of a two-position gang 'switch H2. The connections are such that operation of the switch arm Hz to contacts m, connects condensers C. and Cc in series respectively with condensers Cxand Cy across the respective coils Lx and Ly. Operation of the switchto position n, disconnects condensers Cx and Cc and substitutes therefor a common coupling condenser Cb interposed between the grounded terminals of coils Lx and Ly and the tuning condensers Cx and Cy, being thereby serially included in each of the parallel resonant circuits Lx, Cx and Ly, Cy.-

lThe resonant circuits Lx, Cx, Ca and Ly, Cy and Cc resulting from operation of switch H2 to position m, are loosely coupled capacitively, inductively,.or by a combination of the two, due to their exposed proximity, asis indicated' lat M. For the latter condition coils Lx and Ly are preferably so poled that the inductive coupling aids the capacitive coupling to give the resulting coupling M. If the inductive coupling is madev to oppose the capacitive coupling, the latter must be suiilciently large to assure the desired degree of resulting couplingM. Coupling M, being less ,than optimum, provides a single humped, sharply peaked resonance characteristic for this system,

such as is illustrated by lcurve k of Fig. 2.

With switch Hz operated to contacts n, condensers Cx and Cc are, as stated, replaced by the single coupling condenser Cb, common both to the input Lx, Cx and output Ly, Cy circuits of the coupling system. Condenser Cb is of such magnitude as to produce the relatively broad, double humped, resonance for the coupling system, such as characterizes over optimum coupling illustrated by curvel of Fig. 2.

In order to assure that the resonance bands l and k, Fig. 2, will be symmetrically disposed relatively to the intermediate frequency f, for both positions of switch H2, the following preliminary adjustments are made: with the switch in position n, the coupling condenser C11 is adjusted to give the desired over optimum coupling, curve l, assuring a broad band width for high fidelity in reproduction in the absence of interference. Condensers Cx and Cy are then varied to allocate the intermediate frequency f substantially at the center of the resonance band. Switch Hz is thereupon shifted to position m, to provide the highly selective resonance band, curve k, and condensers Ct and C varied to dispose this narrow resonance band symmetrically with respect to the intermediate frequency f. v

Condenser 2|, interposed between coil Lx and ground I3, is of a sufficiently large capacity not to enter into the high frequency operation of the system. It is merely a blocking condenser which vserves to prevent short circuiting the grounded plate voltage I2 supplying tube V1, and also to isolate this plate voltage from the grid of tube V: likewise grounded at I3 through coil Ly.

In the event that it is desired to apply automatic volume control to the grid of tube V2, a second blocking condenser will bel required in the connection 22 extending from the lower terminal of coil Ly and ground I3. The precise connections for this are illustrated as applied to coupling system T1. An automatic control biasing connection extends from the rectifier output over conductor 23 to the grid of tube V1 through coil Ly'. The alternating current components of the biasing voltage thus applied are illtered out to ground at 8 through the blocking condenser 24 of coupling system T1. Blocking condenser 25 isolates battery 6 from ground 8.

Coupling system T1 is in all respects identical in construction and operation with T2 and may be actuated by a unitary control U, simultaneously and similarly to adjust both coupling systems either to the narrow response, curve k, or to the broad response, curve l. For thev latter condition the common coupling condensers Cb and C11 should be so selected that the maximum coupling does not 'greatly exceed the over optimum condition unless precautions are taken to reduce the tendency of the resulting peaks in the overall response curve to emphasize the extreme modulation frequencies. If, however, this condition is found to be present with the desired coupling, it may be minimized or`elminated by employment of suitable terminating resistances connected in shunt to or included in coils L11'. Ly', etc., in accordance with-well understood illter theory. Alternatively a third coupling system permanently adjusted to the narrow response, curve k, might be associated with the output of tube V2, and adjusted so that the peak of curve k provided by his coupling will fill out the depressions occurring between the peaks, curve l, in the response produced by couplings T1 and Ta. The coupling system of Fig. 3, which is of the same type as that of Fig. 1, provides three adjustments in band width; effected by actuating the gang switch H to positions m, o, and n. With the switch in position m, the tuning condensers Cx and Cy, are connected in series with condensers C11 and Ce respectively, across the respective coils Lx and Ly. With the switch adjusted to position o, the tuning condensers Cx and Cy are connected in series respectively with condensers Cd justed to give the desired maximum or over optimum coupling, and condensers C11 and Cy adjusted symmetrically to dispose the resonance band relative to the intermediate frequency. With the switch in position m for loose or less than optimum coupling, condensers C. and Cc are adjusted to tune the system to the carrier frequency. With the switch in position o, condenser C1 is adjusted to give a desired coupling intermediate to that of switch positions m and n, and

condensers C11 and C. varied to tune the system to the intermediate frequency.

'Ihe Fig. 3 type of coupling system as well as those described below may be employed in a receiver such as is illustrated in Fig. l, by connectare conductively joined by grounded at 21.

ing lead Il to the grid of a succeeding tube, and leads I and B+ to the anode and plate supply respectively of a preceding tube in the manner` illustrated in Fig. 1.

Figs. 4 and 5 show coupling systems wherein 5 the resonance band width is adjustable in steps by means of inductances such as L11-Lc incl., replacing capacities such as C11-Cc incl. in the Fig. l coupling system.

\ Referring to Fig. 4, operation of switch H to 10l positiony 1n. connects coils Lx and L11 in series across condenser Cx, and coils Ly and L11 in series across condenser Cy. The coupling between coils Lx and Ly, onbetween coils La and Lc, or between both mentionedpairs of coils, is then adjusted to l5 give the desired value to pro-vide the narrow band l resonance, such ascurve lc of Fig. 2. With the switch thrown to position n to replace coils L11 and Lc by the common coupling coil Ls, the latter is adjusted to the desired value for the expanded or over optimum coupled condition of curve l, Fig. 2. Condensers Cx and Cy are then adjusted properly to center the band with respect to the carrier frequency f, Fig. 2. The switch is again thrown to position and the narrow band resonance properly centered with respect to the carrier frequency by adjustment of coils L11 and Lc.

Fig. 5 shows the Fig. 4 coupling system as modied by the employment of a two-winding coupling transformer Le', the low potential terminals of which are connected through a lblocking condenser 2l serving to isolate from the secondary circuit Ly, Cy the plate voltage applied over the B+' lead to the primary circuit Ly, Cx. 35 Otherwise the construction and adjustment of the Fig. 5 circuit is similar to thatof Fig. 4.

In the `quantity production of radio receivers employing coupling systems like those of Figs. 4 and 5, coils L1, L11 and Le or Le' would normally be 40 adjustable only in an experimental model for purposes of determining the proper -settings. The usual commercial tolerances are clo-se enough so that the inductances of these coils would not require adjustment as to each receiver. I

Fig. 6 illustrates diagrammatically a coupling system employing a variable condenser D of unique construction adapted to vary the resonance band width by continuous gradations while maintainingV the band symmetrically disposed with respect to the carrier frequency in the manner of curves k and l, Fig. 2. This condenser,A the mechanical assembly of which, Figs.

9 and l0, is described below, is shown diagrammatically in Fig. 6, by the spaced plates q, r, s, t, u inclusive. Plates r and t which are insulatedly mounted stator plates, interleave respectively, variable plates q, s and u, indicated in Fig. 6 for clarity of explanation as being vertically adjustable, whereas as mechanically em- 60 bodied, Figs. 9 and 10., these plates -are rotatablel nant input circuit comprising coil Lx shunted by C5 a tuning condenser Cx, the low-potential end of which is grounded at I3 through blocking condenser 2|. Stator plate t-is joinedv to the highpotential terminal of a resonant output circuit comprising a coil Ly shunted by a tuning con- 70 denser Cy, the low-potential end ofwhich is likewise grounded at I3. Rotor plates q, s and u a conductor 2G It will be observed lthat the capacity -`present r and t.

mined by the overlapping of adjustable plates between stator plates r and t forms a capacitive coupling Cr-t serially interposed between the tuned parallel resonant circuits Lx Cx and Ly Cy. The magnitude of this coupling depends upon the extent to which the interposed, grounded, vertically adjustable plate s, interleaves stator plates The capacities Cq-r and Cir-'5, deterq and s and sta-tor plate r, are eifectively in parallel to each other and to the tuning condenser Cx. Similarly the capacities Cs-r/ and Cu-t between the adjustable plates s and u and the stator plate t respectively, are in parallel to each other and to the tuning capacity Cy.

If now it be assumed that the capacity Cr-i' is increased but without changing the direct capacity from plates 1" and t to ground, the coupling Cr-t will increase with consequent broadening of the resonance band, the latter becoming double humped as optimum coupling is passed. This broadening of resonance will, however, be accompanied by a shifting of the resonance band toward -lower frequencies. If, however, this increase in Cr-i Ais accomplished by the downward movement of plate s there will be a consequent decrease in the capacities Cr-s and Cs-t. the effect of which tends to shift the center of the resonance band toward the higher frequencies. Since the spacing between the plates rs and s-t is less than the spacing between-plates r and t, the latter effect will predominate, and the4 resulting shift in the center of the resonance band will be toward the higher frequencies.

On the other hand, simultaneous vertical movements of plates q andv u to increase the capacities Cq-y and C11-i will tend to shift the resonance band J toward lower frequencies. Therefore, if plates q and u are properly spaced in relation to plates r and-t respectively, and are' further moved simultaneously with plate s, as by employing a rigid connection 26, the tendency toward a shifting vof the resonance band in frequency caused by movement of plate s, may be substantially compensated throughout the con? denser range, by the opposite tendency resulting from the simultaneous movement of plates q and u. In this way the width of the resonance band may be varied without, any substantial sluiting of its median frequency. As mechanically embodied, Figs. 9 and 10, condenser Dis of rotary interleaving plate construction; Stator plates 1' and t are insulatedly supported on rods 36, 31 and 3B, 39, respectively, ex-' tending in insulate'drelation through relatively large apertures 4l)l 'of housing Il, and thence through insulating side blocks, such as. I2. 43 and 44, riveted to opposite outer surfaces of the housing as shown. Rotor plates q, s and u are ,conductively mounted on a rotatable shaft 45, projecting through apertures of the housing Il to .provide bearing supports. Therotor and stator Fig. 6, may be obtained-with a condenserV employing a plurality of plates corresponding tol cach The same results may, however, be y Operation of the Fig. 11 coupling system is the same as that described for the Fig. 6 system. In Fig. 11 the capacity Cq-r represents the sum of the capacities present between plates q1, n; ri, q1; and q2, rz; capacity Cr-s is the sum of the capacities between plates r2, s1; n, sa; and n. sa; the I capacity Cr-i isi that between plates rz, t1; n, t1; and r3, t2; the capacity Ci-t that between plates s1, t1; sa. t1; and sa, tz; and the capacity Cu-t that between plates tz, ui; tz, u1; and ts. ui.

The coupling systems of Figs. 1, 3, 4, and 5 are of the type generically illustrated inFig. '1,-wherein the common coupling impedance Zt is serially included in each of the parallel resonant side cir'- cuits Lx Cx and Ly Cy. Increasing the reactance of Zb, therefore, increases the coupling and tends increasingly toconnect the two side circuits Lx Cx and Ly Cy in series with each other. In orderto secure the relatively narrow band selectivity of Fig. 2, impedance Zb would, at the tuned frequency, normally be relatively small in comparison with the componentl tuning impedances Y of the side circuit reactances. Thus if Zb is an inductance, it would normallyvbe small in comparison with Lx and Ly, and if a capacity, it would normally be large in lcomparison with Cx and Cy.

' The coupling systems of Figs. 6 and 11, on the other hand, are of the type illustrated gen'- erically in Fig. 8, wherein the coupling impedance Zt is serially interposed between the parallel resonant side circuits Lx Cx and Ly Cy. It will be evident that as Zh is decreased the side circuits Lx Cx and Ly Cy are coupled increasingly in parallel with each other. For this case the impedance Zt is, at the tuned frequency, normally large in comparison with the component side circuitreactances. Thus if Zt is an inductance adapted to provide the relatively narrow band selectivities of Fig.'2, it should be large in` com-A Cx and Cy. y

In applying a plurality of coupling systems such as those of Figs. 6 and 11 to a radio broadcast receiver such as Fig. 1, the rotor elements of all of condensers D are preferably manipulated by a unitary control, That is, referring to Figs. 10 and 12, the rotor elements of the several coupling condensers would be mounted on the common shaft.,45.

The coupling systems described herein are notl restricted as to the number of resonant or tuned circuits that may be employed in each. Although the speciiic illustrations are those wherein a pair of resonant circuits are coupled in accordance with the various modicationsof the present invention, the same principles apply in combining three, four or more tuned circuits in each coupling system.

I claim:

1. A high frequency coupling system comprising a plurality of reactively coupled resonant cirparison with the inductances Lx and Ly, and if f a capacity, it should be small in comparison with.

cuits including reactance means of opposite and tuned to a selected frequency, means for adjusting the reactive coupling between said circuits to vary the resonance band width o! saidsystem and for simultaneously altering the reactance value of reactance means of a given type electrically independent and individual to said circuits to prevent shifting ofA the resonance band inthe frequency scale.

2. A high frequency coupling system comprising a plurality of reactively coupled resonant circuits including reactance means of opposite types and tuned to a selected frequency, means for adjusting the reactive coupling between said circuits to vary the resonance band width of said system by continuous gradations and for simultaneously altering the reactance value'of reactance means in each of said circuits to prevent shifting of the resonance band in the frequency scale.

3. A high frequency coupling system comprising a plurality of reactively coupled resonant circuits including reactance means of opposite types and tuned to a selected frequency, means for adjusting the reactive coupling between said circuits to vary the resonance band width of said system to one o1 at least three different values and for simultaneously altering the reactance value of reactance means in each of said circuits to prevent shifting of the resonance band in the frequency scale.`

4. In a. high frequency coupling system comprising a plurality of resonant circuits, each containing inductance and capacitance and tuned to a selected frequency, said circuits being capacitively coupled, means for adjusting the capacitive coupling between sadcircuits to vary the resonance band Width of said system and for altering only the capacitance of each of said `circuits by substituting for capacitance thereof capacitance of adifferent value so as to prevent simultaneous shifting of the resonance band in lthe frequency scale.

5. In'a high frequency coupling system comy prising a plurality of resonant circuits, each containing inductance and capacitance and tuned to a selected frequency, said circuits being inductively coupled, means for adjusting the inductive coupling between said circuits to vary the resonance band width of said system and for altering only inductance of each of said circuits by substituting therefor inductance of a different value so as to prevent simultaneous shifting of the resonance band inthe frequency scale.

6. A high frequency coupling system tuned to a selected frequency comprising: a plurality of reactively coupled resonant circuits, a plurality of supplemental coupling reactances and associated switching means for adjusting said coupling in steps, and supplemental reactances individual to said resonant circuits selectively connectible thereto by said switching means to prevent shifting of the resonance band in the frequency scale with adjustment of said coupling.

'1. A high frequency coupling system tuned to a selectedfrequency comprising: a plurality of reactively coupled resonant circuits each containing inductance and capacity, a plurality of coupling capacities and associated switching means for adjusting said coupling in steps, and supplemental capacities individual to said resonant circuits selectively connectible thereto by said switchi g means to prevent shifting of the resonance band in the frequency scale `with variation in coupling.v A

I 8. A high frequency coupling lsystem tuned to a selected frequency comprising: a plurality oi.' reactively coupled resonant circuits each containing inductance and capacity, a plurality of coupling inductances and associated `switching means for adjusting said coupling in steps, and supplemental inductances individual to said resonant circuits selectively connectible thereto by 5 said switching means to prevent shifting of the resonance band in the frequency scale with said coupling adjustment.

9. A high frequency coupling system tuned to a selected frequency comprising: a pair of similar resonant circuits each containing inductance shunted, by a capacity, adjustable means capacitively coupling said circuits for varying the resonance band width of said system, and means actuated by the couplingadjustment for so altering said shunt capacities 'in relation to said capacitive coupling as to maintain said resonance, band disposed in substantial symmetry with respect to said selected frequency.

10. A high frequency coupling Asystem tuned to a selected frequency comprising: a pair of parallel resonant circuits containing a coimnon coupling reactance serially included in each circuit,` said coupling reactance being relatively small compared to the component tuning reactances of said resonant circuits, and means for simultaneously altering said coupling reactance and component reactances electrically independent and individual to said resonant circuits to vary the band width of said coupling system while preventing shifting of the resonance band in the frequency scale.

11. A high frequency coupling system comprising a p air of parallel resonant circuits containing a common coupling inductance serially included in each circuit, each said resonant circuit containing an individual and electrically independent tuning inductance which is relatively large compared to said coupling inductance, and means for adjusting said coupling inductance to vary 40 the resonance band width of said system and simultaneously adjusting said individual inductances to prevent shitting of the resonance band in the frequency scale.

12. A high frequency coupling system comprisingl a pair-of parallel resonant circuits containing a common coupling capacity serially included in each circuit, each said resonant circuit containing a tuning capacity which is small compared to said coupling capacity, and means for adjusting said coupling capacity to vary the resonance band width of said system and simultaneously adjusting said tuning capacities to prevent shifting 'of the resonance band in the 55 frequency scale.

13. A high frequency coupling system comprising a pair of parallel resonant circuits serially connected through a common coupling reactance,

-said coupling reactance being relatively large compared to component tuning reactances of said 6U' resonant circuits, and means for adjusting said coupling reactance to vary the resonance band width of said system and simultaneously adjusting a component reactance of each of said resonant circuits to prevent shifting of the resonance vary the resonance band width of said system and simultaneously adjusting saidv resonant cir.l 76

nance band in the frequency scale.-

15. A high frequency coupling system tuned to a selected frequency comprising: an interleaving plate condenser consisting of a plurality of aligned stators having certain of their plates mutually exposed capacitively, a rotor common to said stators provided with aligned plates interleaving the mutually exposed stator plates, and angularly displaced therefrom Aon a common shaft other aligned plates capacitively coupled only to plates of the respective stators, aplurality of resonant circuits connected respectively between said stators and the rotor, said rotor and statork plates being so spaced and the said rotor plates so angularly displaced that adjustment of the rotor -varies the resonance band width of said system while preventing shifting of the resonance band in the frequency scale.

16. A high frequency coupling system tuned to a selected frequency comprising: an interleaving plate condenser consisting of'a pair of aligned stators having certain of their plates mutually exposed capacitively, v and `a rotor including aligned plates interleaving the exposed stator plates, and angularly displaced therefrom on a common shaftother aligned plates capacitively coupled only to plates of the respective stators, a pair of resonant'circuits connected respectively between said stators and the-rotor, said rotor plates being so disposed and spaced that adjust-- ment of the rotor varies the resonance band Width of said system while preventing shifting of the resonance band in the frequency scale.

17. A high frequency coupling system tuned to a selected frequency comprising: an interleaving semi-circular plate condenser consisting of a pair of aligned stators having certain of their plates mutually exposed capacitively, and a rotor having aligned plates interleaving the exposed stator plates. and -oppositely displaced therefrom on a common shaft other aligned plates capacitively coupled only to the plates of the respective stators,

la pair of resonant circuits connected respectively between said stators and the rotor, said rotor and stator plates being so spaced that adjustment of the rotor varies the resonance band width of said system while preventing shifting of the resonance band in the frequency scale.

18. A high frequencycoupling system tuned to a selected frequency comprising a variable interleaving plate condenser consisting of a rotor having a pair of aligned plates angularly displaced on a shaft with respect to an intermediate plate, and a pair of insulatedly supported stator plates spaced to interleave the rotor plates, and a pair of resonant circuits connected respectively between the stator plates and the rotor, said plates being so spaced, shaped and angularly displaced that adjustment of the rotor varies the resonance band width of said system while preventing shifting the resonance band in the frequency scale.

19. A high frequency coupling system tuned to a selected Yfrequency' comprising: aninterleaving semi-circular plate condenser comprisinga rotor consisting of a pair of aligned plates angularly displaced on a conductive shaft with respect to an intermediate plate, a pair of insulated stator plates spaced to interleave the rotor plates, a pair of resonant circuits connected between the respective stator plates and the rotor, said rotor and stator plates being so spaced and the said rotor plates being so angularly displaced that adjustment of the rotor varies the resonance band j cuit capacities to prevent shifting of the reso-v width of said system while preventing shifting of the resonance band in the frequency scale.

20.. In'a high frequency .coupling system comprising two resonantcircuits tuned to a selected frequency and adapted to be adjustably coupled 5 to permit variation of the resonance band width of said 'system without shifting the resonance band in the frequency scale, a variable coupling con-denser therefor of rotary interleaving plate construction comprising: a plurality of insulatedly supported aligned stators having certain of their plates mutually exposed capacitively, a rotor common to said stators provided with yaligned plates interleaving the mutually exposed stator plates, and angularly displaced therefrom on a common shaft other alignedplates capacitively coupled only to plates of the respective stators; the rotor and stator plates being so spaced and shaped and the said rotor plates being so .angularly displaced that adjustment of the rotor to increase the capacity between said stators decreases in va definite relation thereto the capacities between the rotor and the respective stators. 21. In a high frequency coupling system comprising two resonant circuits tuned to a selectedy frequency and adapted to be adjustably coupled to permit variation of the resonance band width of said system without shiftingl the resonance band in the frequency scale, a variable coupling condenser therefor of rotary interleaving plate construction comprising; a pair of insulatedly supported aligned stators having certain of their plates mutually exposed capacitively, a rotor common to said stators provided with aligned plates interleaving the mutually exposed stator plates, and angularly displaced therefrom on a common shaft other aligned plates capacitively coupled only to plates of the respective stators, said rotor' and stator plates being so spaced and the said rotor plates being so angularly displaced that adjustment of the rotor varies the capacities between said stators in definite relation to the capacities between the rotor and the respective. stators.

22. In a high frequency coupling system comprising two resonant circuits tuned to a selected frequency and adapted to be adjustably c pled to permit variation of the resonance band dth of said system without shifting the resonance band in the frequency scale, a' variable coupling condenser therefor comprising: a rotor having a pair of aligned plates angularly displaced on a common'shaft with respect to an intermediate plate, and a pair of insulatedly mounted stator plates interleaving the rotor plates, said rotor and stator plates being so spaced and shaped and the saidv rotor plates being so angularly displaced that adjustment of the rotor to increase capacity be- Y value to prevent shifting of -theresonance band in the frequencyscale by the adjustment of said coupling.

24. A high frequency coupling system comprising a plurality of reactively coupled resonant circuits including reactance means of opposite tvpes and tuned to a selected frequency, means for adjusting the reactive coupling of only one type between said circuits to vary the resonance band width of said system and for simultaneously altering the reactance value of reactance means, of the same type as said adjusted coupling reactance, in each of said circuits, to prevent shifting of the resonance band in the frequency scale by the adjustment of said coupling.

25. A high frequency coupling system comprising: a plurality of resonant circuits including reactance elements of opposite types tuned to a selected frequency and coupling reactance of a given type coupling said circuits, means for adjusting the resonance band width of said system comprising means for substituting for a coupling reactance element in at least one of said circuits a band width of said system comprising means for substituting for a couplingV inductance element in at least one of said circuits a supplemental inductance providing a diierent value of reactance in said circuit, whereby simultaneous shifting o! the resonance band in the frequency scale is prevented.

DANIEL E. HARNETI. 

